.... I've found it to be great for individual portraits and even a good travel lens when I don't want to lug my 70-200mm f2.8L around. I've attached some example photos from it.
Nice shots, Are those all at f2.8?
Wide angle zoom lens designs for a FF image circle are more difficult than telephoto zoom designs - the fact that the 70-200/4 and the 17-40/4 are close in price is consistent with the 17-40 needing more optical compromises and suffering lower IQ for them. It has a LOT of barrel distortion, and at wide apertures, especially at the wide end, the corners are a mushy mess. Not sure if one of the EF-S lenses you sold was the 10-22mm, but the small image circle makes a huge difference - for the same cost, the 10-22 delivers much better optical performance (rivals the 16-35 II except for the slower aperture).
Now, the 17-40mm isn't all bad - like any piece of gear, if you know its limitations and how to work around them, you can get good results. For example, don't shoot architecture at 17mm. Generally, if you shoot the 17-40mm at 20mm or narrower and stopped down to f/8-f/11 (e.g. landscapes from a tripod), it's fine. If you plan to shoot at 17mm f/4 a lot, you'll likely be disappointed. So...good as a landscape lens, not so good as a walkaround lens (for which I'd really recommend the 24-105mm, as 24mm on FF is wide enough for many needs (equivalent to 15mm on crop). But, the best time to get the 24-105 is with the 5DII as a kit, when you pay just $800 for the lens.
Have you considered renting for your Hawaii trip, perhaps the 16-35 II?
That's some useful information to have and understand when looking to buy a wide angle for a full frame, I had never considered that the size of the sensor can contribute to that distortion on the corners, I guess shouldn't be a surprise though as vignetting is a more of an issue on FF for similar reasons.
I was hoping to take advantage of some of the rebates that now expire on Feb 7th but I might not want to rush into this, renting for my trip isn't a bad idea, as nothing is better than actually having shot with that lens to give you confidence when you click "checkout".
As far as a walk-around lens, I do see a 24-105L in my future at some point, I noticed that the used market has been pretty well stocked with them, and most are new (parted out of a 5dmk2 kit) and thats driving the actual used ones down even further in price, so I might grab one at some point. The new prices on those primes were the used prices a few months back, and that ridiculous sharpness and IQ of the 135L is fresh on my mind. But the 24-105L might just be my best bet for the time being, 24 on a FF is plenty wide for a lot of shots.